1. Field of the Invention
The present invention is generally directed to the field of semiconductor processing, and, more particularly, to a method of removing photoresist from above a surface of a process layer formed above a surface of a semiconducting substrate.
2. Description of the Related Art
In general, semiconductor devices are manufactured by forming many process layers comprised of various materials above a semiconducting substrate, and, thereafter, removing selected portions of the layers, i.e., patterning the layers. This patterning may be accomplished using known photolithography and etching processes to define the various features of the device, e.g., the gate insulation layer, the gate electrode, sidewall spacers, metal lines and contacts, etc. This forming and patterning of the process layers is typically performed layer by layer as the individual layers are formed, although multiple layers may be patterned at any given time.
Photolithography is a common process used in patterning these various layers. Photolithography typically involves the use of a product known as photoresist. In general terms, photoresist is a product whose solubility in a developer may be manipulated by exposure to a light source. There are positive and negative photoresists currently available on the market.
In general, the photolithography process involves forming a layer of photoresist above a previously formed process layer, and exposing selected portions of the layer of photoresist to a light source to form a pattern in the photoresist that is desired to be formed in the under lying process layer. All of these steps are typically performed in well-known photolithography modules that include a section for depositing the photoresist on the wafer, e.g., a spincoating station, a device for selectively exposing portions of the photoresist layer to a light source through a reticle, e.g., a stepper, and a section for rinsing and developing the photoresist layer after it has been selectively exposed to the light source. Thereafter, an etching process, such as a plasma etching process, is performed to remove portions of the underlying process layer that are not covered by the patterned layer of photoresist, i.e., the patterned layer of photoresist acts as a mask. After the etching process is complete, the patterned photoresist layer is removed so that additional process layers may be formed above the now patterned process layer.
One technique used to remove the photoresist is plasma stripping, also sometimes referred to as ashing. During this process, the wafer is placed into a plasma etch tool, and an etching process is performed, typically in an oxygen-based environment, such that the photoresist is oxidized to form gaseous products, which are pumped away. Optical emission spectrometry may be used to detect when this process is complete, or to xe2x80x9cendpointxe2x80x9d the process. Optical emission spectrometry involves detecting different wavelengths of light or energies depending upon the material contained in the reaction product gases of the plasma strip process. The plasma strip process continues until the optical spectrometry analysis indicates that there is no more photoresist being consumed in the process. At that point, the process is deemed complete. Optical emission spectrometry may be used initially in combination with other techniques. For example, a timed etch process may be used to remove the bulk of the layer of photoresist, and optical emission testing may only be performed for the last 10-20% of the photoresist layer to endpoint the process.
Endpointing the photoresist removal process using optical emission spectrometry has many deficiencies. For example, optical emission spectrometry does not provide any spatial information as to differences in rates of removal of the layer of photoresist across the surface of the wafer. That is, using optical emission spectrometry, it is not known whether the photoresist at the edge of the wafer has been completely removed while photoresist remains at the center of the wafer, or vice versa. Moreover, since the endpoint is not signaled until all or substantially all of the photoresist is removed, portions of the underlying process layer in areas where the photoresist has been removed first may be unnecessarily subjected to more of the plasma stripping process than would otherwise be necessary. This situation may be problematic for several reasons. For example, the underlying process layer is undesirably exposed to charged particles in the plasma strip process, and this may lead to electrically charging the exposed surface of the process layer, which can potentially lead to device degradation and yield loss.
The present invention is directed to a method that minimizes or reduces some or all of the aforementioned problems.
The present invention is directed to a method of endpointing photoresist removal processes based upon the temperature of the wafer. In one illustrative embodiment, the method disclosed herein comprises forming a process layer above a semiconducting substrate, forming a layer of photoresist above the process layer, removing the layer of photoresist by performing an etching process, and determining an endpoint of the etching process based upon a temperature of the substrate.